Being billed for a cancelled order nearly 4 months later

I did 2 online purchases in March, the first was cancelled the same day, so nothing was shipped to me. 3 months later and I'm still being asked to make payment on items that never were shipped to me. I'm being billed added interest and receiving calls to make payment, so now my account is suspended. Each time I talk to someone I explain the mistake made by Mr P staff and asked for the correction to be made, but still nohting has progressed. I am happy to pay when my account is corrected, but I cant be expected to pay more than that. I am told calls are recorded but it doesnt look like anything is done with that since nobody in management bothers to follow up and see this through.